This patent relates to the use of hydrophobic polyurethane foam as a backing material for bandages and to bandages made with a hydrophobic polyurethane foam backing. The hydrophobic polyurethane foam is relatively thick. The hydrophobic polyurethane foam permits water vapor to escape from the surface of the skin, but keeps liquid water from reaching the surface of the skin.
It is well known to apply adhesive bandages (also known as wound dressings) to wounds to protect the wound and keep the wound clean. Most commonly, the bandages are made from a polyethylene or polyvinyl chloride backing material. One side of the backing material generally contains a centralized pad, which is utilized to keep the wound clean and to cushion the wound. Adhesives are used alongside the pad to hold the bandage in place. The polyethylene backing material does not allow water vapor to leave the surface of the skin covered by the bandage. This leads to discomfort for the user. In order to overcome this problem, bandages generally are apertured, that is, the polyethylene film is perforated to allow water vapor to leave the surface of the skin.
Although apertured films are useful, there is a concern that the apertures allow liquid water to reach the surface of the skin and the wound. The presence of water promotes bacterial growth, which can lead to an infection of the wound. Therefore, there is a need for a bandage that allows water vapor to evaporate from the surface of the skin under the bandage (is “breathable”), but does not let liquid water reach the surface of the skin under the bandage (is “waterproof”).
The use of thin breathable films, such as 0.025 mm polyurethane as the backing material for a wound dressing has been practiced since the 1970s. U.S. Pat. No. 3,645,835 disclosed this type of adhesive dressing for blocking bacteria and liquid water from reaching the wound, but allowing oxygen to penetrate the dressing from the atmosphere and allowing moisture from the skin of the patent to escape from beneath the dressing.
The moisture vapor transmission rate (“MVTR”) measures the degree of breathability of a film. In order to obtain the desired MVTR, these types of films are generally thin, ie. less than 0.05 mm in thickness. Because of the nature of polymers used for breathable films, breathable films made at the thickness of 0.05 mm or less are generally flexible, limp, flimsy and hard to handle. When adhesive is applied on the film to enable the film dressing to adhere to the skin, the film tends to stick to itself wherever adhesive surfaces touch each other. This makes it difficult to apply the thin breathable film dressings to the skin.
To overcome this problem, delivery systems have been designed to handle these types of dressings. U.S. Pat. Nos. 4,413,621 and 4,485,809 are two examples. One disadvantage of thin breathable film dressings with delivery systems is that it is sometimes difficult for users to figure out how to use them. Another disadvantage of thin breathable film dressings with delivery systems is that it is sometimes difficult for users to use the delivery system.
Another method to improve the ability to handle thin breathable films was taught in U.S. Pat. No. 4,846,164. The patent taught the use of composites, which combined thin films with other materials. U.S. Pat. No. 4,773,409 also taught the use of composites for bandages. The composites included a polyurethane film and a polyurethane foam containing water dispersible or water swellable agents. Composite bandages are generally more expensive to produce than the thin film. Additionally, the presence of water swellable agents might not be desirable, as the result would be a moist surface against the wound, which would promote bacterial growth, and possibly an infection of the wound.
Therefore, despite the disclosure of the references, there is a continuing need for a bandage that is breathable, but is waterproof, and is easy to handle and apply to a wound.